The problem is that too many shipping lines mothballed vesselsWould it stand to reason that they mothballed the oldest, slowest, least efficient, etc etc etc?
I dunno, just asking. That's how I'd do it.
Of course, less efficient vessels get mothballed first. My point is that shipping companies are more concerned with keeping an artificial shortage so they can keep their capacity tight and their rates up than they are with clearing backlog and serving their customers.
It is sort of like denying a small town the services of what might be a reasonably good GP doctor because he or she is not a competent brain surgeon.